Direct reduced iron (DRI), which is also referred to as sponge iron, is typically produced by the reaction of iron ore in a reactive gas stream containing reducing agents, such as H2 and CO, in a moving bed or vertical shaft reactor. The following are the equilibrium-limited global reactions:Fe2O3+3H22Fe+3H2O  (1)Fe2O3+3CO2Fe+3CO2  (2)
In commercial DR processes, the product DRI still contains unreacted iron oxide, which may be as high as 15.0% by weight. Due to the equilibrium-limited nature of reactions (1) and (2), it is not economical to achieve complete (i.e. 100.0%) reduction within the reduction reactor. In fact, when the degree of reduction approaches 100.0%, an excessively long residence time inside the reduction reactor is required to remove the remaining oxygen from the partially reacted material. While the rate of reduction reactions can be increased to some extent by increasing temperature, such temperature increases are limited by the fact that the operating temperature must be kept below the sintering temperature so that clusters are not formed inside the reduction reactor. Thus, the typical reduction is maintained somewhere in the 85.0-95.0% range at the discharge of conventional commercial reduction reactors, depending on the quality of the oxide material and plant operating conditions.
Such product DRI can be used as a source of low-residual iron, in addition to ferrous scrap and pig iron in the production of steel, mainly through an electric arc furnace (EAF) in a steelmaking facility. The EAF melts that charged material by means of an electric arc, typically accompanied by the injection of oxygen in order to burn impurity carbon and Fe3C, if any. The partial or complete combustion of the carbon with oxygen provides a uniform internal source of energy for the EAF when the oxygen is injected into the EAF. Furthermore, the conversion of Fe3C into iron and carbon is an exothermic reaction, which improves the thermal efficiency of the EAF. Therefore, the carbon content of the DRI can be interpreted as an energy source, and this energy is finally utilized in the EAF when the DRI is melted.
Although other carbon sources, like coal or rubber, can be added to the EAF for the same purpose, the resulting yield is significantly less than the combined carbon in the DRI, due to particle blow-off and impurities in the carbon sources. Therefore, it is highly desirable to increase the carbon content of DRI during the reduction step before discharging it into the EAF.
Inside the reduction reactor, carbon can be generated (i.e. physical carbon—C) or added to the DRI (i.e. chemical carbon—Fe3C) through the following global reactions:3Fe+CO+H2Fe3C+H2O  (3)3Fe+2COFe3C+CO2  (4)3Fe+CH4Fe3C+2H2  (5)CO+H2C+H2O  (6)2COC+CO2  (7)CH4C+2H2  (8)
Therefore, two major sources of combined carbon in product DRI (i.e. physical and chemical) are CO and hydrocarbons (e.g. CH4) in the reducing gas stream. While the amount of CO in the reducing gas stream is normally set by the operating conditions of the reducing gas generation unit, the amount of hydrocarbons is adjusted by the operator to suppress methanation reactions inside the reduction furnace, while considering the cooling effects caused by:                Endothermic reactions (5) and (8) above,        Endothermic reforming reactions catalyzed by iron within the reduction reactor,        Direct heat removal by the hydrocarbons, which have noticeably higher heat capacities as compared to most of the gases in a DR plant, and        Limited preheat temperatures for hydrocarbon streams (below ˜400 degrees C.).In other words, from an operational point of view, there are limitations to increase the amounts of CO and CH4 in the reducing gas stream.        
One of the commercially practiced approaches for bypassing these limitations is the addition of a hydrocarbon-rich stream to the bulk of the already reduced materials. This is usually done by injecting natural gas into the hot reduced material (a good catalyst) once it leaves the reduction zone—a region typically called the transition zone. Thus, due to cracking reactions in the transition zone, the carbon content of the product increases.
Due to the endothermic nature of the cracking reactions, this interaction lowers the material and gas temperatures, thus helping to cool the product DRI. However, this cooling effect for plants where the DRI has to leave the reduction furnace at elevated temperatures, is viewed as a negative side effect, and is typically minimized.
In commercialized DR processes, a hydrocarbon source is normally utilized to produce the reducing agents via a catalytic or non-catalytic reforming process. For catalytic reforming processes, the required oxidants are typically H2O (i.e. steam) and CO2. For non-catalytic reforming processes, the required oxidant is typically oxygen (O2). In the latter case, very fast partial and complete combustion reactions generate H2O and CO2 for further homogeneous and/or heterogenous reforming reactions. All reforming processes convert some portion of the carbon and hydrogen contents of the hydrocarbons into CO and H2, respectively. For instance, in the case of CH4 being the only hydrocarbon source, the global reaction schemes governing the homogenous and heterogenous reforming processes are:CH4+2O2CO2+2H2O  (9)CH4+1.5O2CO+2H2O  (10)CH4+O2CO+H2+H2O  (11)CH4+0.5O2CO+2H2  (12)CH4+H2OCO+3H2  (13)CH4+CO22CO+2H2  (14)The gas leaving the reforming process is therefore a mixture of CO, H2, and unreacted hydrocarbons and oxidants, and is called the reformed gas.
Alongside these main reactions, depending on the thermodynamics of the system, some of the previously mentioned reactions can also occur, the major of which are:CO+H2C+H2O  (6)2COC+CO2  (7)CH4C+2H2  (8)The resulting carbon from these side reactions creates detrimental consequences for the reforming catalyst, and, therefore, it is a common practice to prevent their occurrence by controlling the operating parameters of the reformer unit.
Based on reactions (1) and (2), the presence of oxidants H2O and CO2 in the reducing gas mixture reduces the efficiency of the reduction reactions. Consequently, operating parameters in the reforming section of the plant are adjusted in such a way that the reformed gas has high values of CO/CO2 and H2/H2O, which can be achieved by a high conversion rate for CH4, while maintaining the concentrations of H2O and CO2 to the lowest extent possible in the feed gas to the reforming unit. Typically, CH4 slip from the reformer unit is maintained below ˜1.0-2.0%, and, as a result, similar to CO/CO2 and H2/H2O, the H2/CH4 ratio in the reformed gas stream is high. While a high CO/CO2 ratio in the reformed gas stream favors carbon deposition inside the reduction reactor according to reactions (4) and (7), a high H2/CH4 ratio diminishes the chance of carbon deposition according to reactions (5) and (8). Thus, it is clear that by increasing the CO/CO2 ratio, the carburization potential of the reformed gas improves. This is the main focus of the present invention.